The F28 error code on a Vaillant boiler is one of the most common — and most frustrating — faults homeowners face. It means your boiler has tried to ignite and failed, leaving you without heating and hot water. The good news is that F28 is often caused by a single faulty part that you can replace quickly and affordably.
In this guide, we explain exactly what Vaillant F28 means, the five most common causes, how to reset the boiler, and which spare part you need to fix it for good.
What Does F28 Mean on a Vaillant Boiler?
F28 is an ignition lockout fault. In plain English: your boiler tried to light the gas burner but couldn’t establish a stable flame. After three failed ignition attempts, the boiler locks out and displays F28 on the screen.
This fault appears on most modern Vaillant models including:
- ecoTEC Pro
- ecoTEC Plus
- ecoFIT Pure
- ecoCOMPACT
Important: Do not keep resetting the boiler repeatedly. If F28 keeps coming back, there is an underlying fault that needs fixing.
Cause 1: Faulty Ignition Electrode (Most Common)
The ignition electrode creates the spark that lights the gas. Over time, the ceramic insulator can crack, the metal tip can wear down, or carbon can build up on the surface.
Signs it’s the electrode:
- You hear clicking but no flame
- The boiler lights briefly then goes out
- F28 appears intermittently, especially on cold mornings
Fix: Replace the ignition electrode. On Vaillant ecoTEC models, the electrode is usually located at the front of the burner. We stock genuine and compatible ignition electrodes for all Vaillant ecoTEC and ecoFIT boilers.
Cause 2: Blocked or Wet Burner
If the burner is clogged with debris, dust, or condensation, the gas cannot flow properly and the flame won’t establish.
Signs it’s the burner:
- The boiler has not been serviced in over 12 months
- You can smell gas briefly before the lockout
- Other error codes appear alongside F28
Fix: A Gas Safe engineer should clean or replace the burner. Do not attempt this yourself.
Cause 3: Gas Valve Not Opening
The gas valve controls the flow of gas to the burner. If the valve fails to open or only opens partially, there isn’t enough gas to ignite.
Signs it’s the gas valve:
- No gas smell at all during ignition attempts
- The boiler worked fine until recently, then stopped completely
- Other ignition faults appear (F29, F54)
Fix: Replace the gas valve. This must be fitted by a Gas Safe registered engineer. We stock gas valves for Vaillant ecoTEC Pro and Plus models.
Cause 4: Low or Unstable Gas Pressure
If the gas pressure at the boiler is too low, the flame cannot establish properly. This can be a supply issue or a regulator problem.
Signs it’s gas pressure:
- Other gas appliances in the home are also struggling
- The fault started after gas works in the area
- The boiler works fine on warm days but shows F28 in cold weather
Fix: Check with your gas supplier. If pressure is fine at the meter but low at the boiler, the gas valve or pressure regulator may need replacing.
Cause 5: Faulty PCB (Printed Circuit Board)
The PCB controls the entire ignition sequence. If it’s not sending power to the ignition electrode or gas valve at the right time, ignition will fail.
Signs it’s the PCB:
- Intermittent faults that change each time you reset
- Multiple unrelated error codes
- The boiler works perfectly for days, then fails suddenly
Fix: Replace the PCB. This is a more expensive repair but often cheaper than a new boiler. Always fitted by a Gas Safe engineer.
How to Reset a Vaillant F28 Error
- Press and hold the reset button (usually a flame icon or circular arrow) for 3–5 seconds
- Wait for the boiler to go through its ignition sequence
- If it fires normally, monitor it for 24 hours
- If F28 returns, do not keep resetting it — a part has failed and needs replacing
F28 vs F29: What’s the Difference?
Table
| Fault Code | Meaning | Most Likely Cause |
| F28 | Ignition failed (no flame detected) | Ignition electrode, gas valve, burner |
| F29 | Flame lost after ignition | Flame sensor, flue blockage, gas pressure |
If you see F29 instead of F28, the boiler lit successfully but lost the flame. This usually points to a flame detection electrode or flue issue rather than the ignition electrode.
Which Part Do I Need for F28?
If you’re not sure which part is causing the F28 fault, start with the cheapest and most common fix:
- Ignition electrode — £15–£30, easy to fit
- Flame detection electrode — £15–£25, easy to fit
- Gas valve — £80–£150, Gas Safe only
- PCB — £150–£300, Gas Safe only
We recommend replacing the ignition electrode and flame sensor together if your boiler is over 5 years old. Both parts wear out at a similar rate.
When to Call a Gas Safe Engineer
You should never attempt the following yourself:
- Removing the gas valve
- Working on the burner
- Replacing the PCB
- Any work that involves breaking the gas seal
A Gas Safe engineer can diagnose F28 accurately using a multimeter and gas pressure gauge, saving you from buying the wrong part.
Shop Vaillant F28 Fault Parts
- At Boiler Spares Ltd, we stock Vaillant ignition electrodes
you need to fix the Vaillant F28 error:
All available with fast UK delivery from Huddersfield. Order before 3pm for same-day dispatch on most items.